<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>p4_居中测试</title>

    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .main {
            background-color: cyan;
        }
        .card{
            width: 200px;
            height: 300px;
            margin: 0 auto;
            background-color: pink;
            border: 3px solid #f00;
            text-align: center;
            line-height: 300px;
        }
        .center {
            width: 1000px;
            background-color: #0aa1ed;
            margin: 0 auto;
        }
    </style>

</head>
<body>
<!-- 最外层功能模块 -->
<div class="main">
    <!-- 版心 -->
    <div class="center">
        <!-- 主要的展示内容 -->
        <div class="card">我是内容</div>
        <div class="card">我是内容</div>
        <div class="card">我是内容</div>
        <div class="card">我是内容</div>
    </div>
</div>

</body>
</html>